1. Field of the Invention
The present invention relates generally to mechanical jars that perform impact-related forces on a tool string downhole in hydrocarbon wells, water wells, or other well applications.
2. Description of the Related Art
Well operations often require the use of devices that provide an “impact” on a tool string or a downhole production device. Certain types of downhole tools require the shearing of screws or pins to either set or release a device. A downhole packer or bridge plug, for example, may be run into a wellbore on wireline and then set in place within the is wellbore by shearing screws on the run-in tool. To do this, an impact load will need to be delivered to the run-in tool that is sufficient to cause shearing to occur. In other applications, a device that is being installed in or removed from a production string by wireline or coiled tubing may require impacts to properly install or remove it. For example, gas-lift valves are typically installed in and removed from the pocket of a gas-lift mandrel by a wireline tool. Removing the gas lift valve from the pocket requires the application of an impact force to unseat the valve from the pocket.
Typically, a mechanical, hydraulic or spring-type jarring tool is used to deliver the impact forces for these situations. With these tools, the impact force is predetermined and calibrated at the surface prior to running the jarring tool in to the wellbore. However, the actual impact force that will be delivered while in the hole will vary depending upon the various well environments and geometries that exist. One important aspect of wellbore geometry is wellbore angle or deviation. Wellbore deviation applies increased friction forces on the tool string and thereby results in reduced impact forces being applied by the jarring tool. In particular, spring jars require pre-set calibration at the surface by manually applying torque to the spring mechanism prior to running the tool in. However, this is not optimal where the wellbore angle is unknown or if wellbore angle changes along the length of the wellbore.